Various processes and catalysts exist for the homopolymerization or copolymerization of olefins. For many applications, it is desirable for a polyolefin to have a high weight average molecular weight while having a relatively narrow molecular weight distribution. A high weight average molecular weight, when accompanied by a narrow molecular weight distribution, provides a polyolefin with high strength properties.
Traditional Ziegler-Natta catalysts systems comprise a transition metal compound co-catalyzed by an aluminum alkyl and are typically capable of producing polyolefins having a high molecular weight, but with a broad molecular weight distribution.
More recently metallocene catalyst systems have been developed wherein the transition metal compound has one or more cyclopentadienyl, indenyl or fluorenyl ring ligands (typically two). Metallocene catalyst systems, when activated with cocatalysts, such as alumoxane, are effective to polymerize monomers to polyolefins having not only a high weight average molecular weight but also a narrow molecular weight distribution.
Metallocenes containing substituted, bridged indenyl derivatives are noted for their ability to produce isotactic propylene polymers having high isotacticity and narrow molecular weight distribution. Considerable effort has been made toward obtaining metallocene produced propylene polymers having ever-higher molecular weight and melting point, while maintaining suitable catalyst activity. Researchers currently believe that there is a direct relationship between the way in which a metallocene is substituted, and the molecular structure of the resulting polymer. For the substituted, bridged indenyl type metallocenes, it is believed that the type and arrangement of substituents on the indenyl groups, as well as the type of bridge connecting the indenyl groups, determines such polymer attributes as molecular weight and melting point. Unfortunately, it is impossible at this time to accurately correlate specific substitution patterns with specific polymer attributes, though minor trends may be identified, from time to time.
For example, U.S. Pat. No. 5,840,644 describes certain metallocenes containing aryl-substituted indenyl derivatives as ligands, which are said to provide propylene polymers having high isotacticity, narrow molecular weight distribution and very high molecular weight.
Likewise, U.S. Pat. No. 5,936,053 describes certain metallocene compounds said to be useful for producing high molecular weight propylene polymers. These metallocenes have a specific hydrocarbon substituent at the 2 position and an unsubstituted aryl substituent at the 4 position, on each indenyl group of the metallocene compound.
Also known in the art are unbridged indenyl based metallocenes having bulky substituents on the indenyl ligand, thus providing “fluxionality” to the activated catalyst. Metallocenes of this type are believed to produce “elastomeric” polypropylene. Science, 1995, 267, 217; WO 95/25757; and Organometallics, 1997, 16, 3635 discuss such catalysts.
In addition to hydrocarbon substituents, it is also known to include halogen substituents on metallocene compounds. For example, U.S. Pat. No. 3,678,088 discloses polychlorinated metallocenes having formulae C5H5-mClmMC5H5 and (C5H5-nCln)2M wherein M is iron, ruthenium or osmium, m is an integer from 3 to 5, inclusive and n is an integer from 2 to 5, inclusive. There is no disclosure of the polychlorinated metallocenes being used as olefin polymerization catalysts.
Similarly, chlorinated metallocenes including (CpCl)2TiCl2, (CpCl)(Cp)TiCl2, (CpCl)2TiClMe, and (CpCl)(Cp)TiClMe are disclosed in J. Am. Chem. Soc. 1988, 110, 2406; J. Organometallic Chem. 1988, 358, 161; Organometallics 1985, 4, 688 and Electrochimica Acta, 1995, 40, 473.
U.S. Pat. Nos. 5,504,232, 5,763,542 and 6,087,292 disclose olefin polymerization catalysts based on bridged halogen substituted indenyls of Groups 4-6, such as Zr and Hf. Particularly exemplified are rac-dimethylsilanediylbis(5(6)-fluoroindenyl) zirconium dichloride (F mixed in 5 and 6 positions), rac-dimethylsilanediylbis(5-chloroindenyl)zirconium dichloride, rac-dimethylsilanediyl bis(4(7)-fluoroindenyl) zirconium dichloride (F mixed in 4 and 7 positions), and rac-dimethylsilanediylbis(5,6-dichloroindenyl)zirconium dichloride.
JP1999-080183A discloses halogenated substituents on racemic carbon bridged bis-indenyl Group 4 transition metal complexes. The application focuses on the use of these complexes as pre-catalysts for the copolymerization of vinyl aromatic monomers (styrene). The only complexes exemplified are isopropylidene-bis(5- or 6-fluoroindenyl) zirconium bisdimethylamide, isopropylidene-bis(5- or 6-fluoroindenyl) zirconium dichloride, isopropylidene-bis(5-chloroindenyl) zirconium bisdimethylamide, and isopropylidene-bis(5-chloroindenyl) zirconium dichloride. The application gives preference to F>Cl>Br.
JP1995-216011A discloses olefin polymerization catalysts comprising bridged bis-indenyl Group 4-6 transition metal complexes, having halogen substituents either in the 2 or the 7 position on the indene ring. However, the only complexes exemplified are bridged bis-indenyl complexes having a fluoro- or chloro-substituent at the 7 position and a hydrocarbyl or substituted hydrocarbyl substituent at the 4 position.
U.S. Patent Application Publication No. 2004/0260107, published Dec. 23, 2004, discloses a large number of bridged indenyl substituted cyclopentadienyl complexes of Group 3 to 6 metals and indicates that the complexes are useful as olefin polymerization catalysts. Among the complexes specifically disclosed, but not synthesized, are dimethylsilanediyl(2-methyl-4-phenyl-7-chloroindenyl)(2-isopropyl-4-phenylindenyl)zirconium dichloride, dimethylsilanediyl(2-methyl-4-phenyl-7-bromoindenyl)(2-isopropyl-4-phenylindenyl)zirconium dichloride, dimethylsilanediyl (2-methyl-4-(1-naphthyl)-7-chloroindenyl)(2-isopropyl-4-(1-naphthyl)indenyl)zirconium dichloride, dimethylsilanediyl(2-methyl-4-(1-naphthyl)-7-bromoindenyl) (2-isopropyl-4-(1-naphthyl)indenyl)zirconium dichloride, dimethylsilanediyl(2-methyl-4-(p-t-butylphenyl)-7-chloroindenyl)(2-isopropyl-4-(p-t-butylphenyl)indenyl)zirconium dichloride and dimethylsilanediyl(2-methyl-4-(p-t-butylphenyl)-7-bromoindenyl)(2-isopropyl-4-(p-t-butylphenyl)indenyl)zirconium dichloride.
U.S. Patent Application Publication No. 2002/0193535 discloses a process for polymerizing propylene in the presence of a Group 3-5 transition metal catalyst having two indenoindolyl ligands, wherein the term “indenoindole” is defined to mean an organic compound that has both indole and indene rings in which the five-membered rings from each are fused. The indenoindole rings can be substituted with a variety of moieties, including halogen, and specifically disclosed and exemplified is bis(2-chloro-5-phenyl-5,10-dihydroindeno[1,2-b]-indolyl)zirconium dichloride.
Fluorinated bisindenyl metallocenes, particularly bis(4,7-difluoroindenyl) zirconium dichloride and bis(4,7-difluoroindenyl)zirconium dibenzyl, and their use in olefin polymerization are discussed in Organometallics, 1990, 9, 3098.
Brominated fluorenylcyclopentadienyl metallocenes, particularly (2,7-dibromofluorenyl)(cyclopentadienyl)zirconium dichloride, (2,7-dibromofluorenyl) (cyclopentadienyl)zirconium dimethyl and (2-bromofluorenyl)(cyclopentadienyl) zirconium dichloride, and their use in olefin polymerization are discussed in J. Organometallic Chem., 1995, 501, 101.
It will be seen that the focus of existing research into halo-substituted metallocenes has been on compounds having two cyclopentadienyl, indenyl and/or fluorenyl ligands. However, since the effects of various substituents on the polymerization properties of metallocene catalysts is still largely an empirical matter; there is a continued interest in synthesizing and testing new metallocene structures.